The present invention relates to a reversible memory structure, i.e. it can be thermo-optically written and erased, whilst reading is optical.
It applies more particularly to the inscription or writing layer of a memory storing data on a moving support. One widely used form of this memory is the optical disk. Optical disks are made from a disk of a rigid and generally transparent material covered with a thin film of a light-absorbing material. The disk rotates at a relatively high speed and passes in front of a reading head, which detects the data which have been recorded in the surface absorbent layer. The data are generally stored in the form of perforations in the absorbent layer. Thus, reading can take place by passing a laser beam through the data storage holes and through the transparent support of the optical disk. It can also be carried out by reflecting a laser beam through the transparent support of the disk onto the absorbent layer. The data can also be stored in the form of a surface deformation in which case reading takes place by reflection.
The existing technology of optical disks or in more general terms moving memories has two types of structure for the writing or inscription layer, namely non-erasable structures such as those in which are made perforations of the metal layer constituting the absorbent layer, or erasable structures. Erasable structures are based on the use of amorphous, metallic or semiconducting materials or magnetooptic, photochromic or photodichroic materials having differences in the optical properties depending on whether or not they are inscribed by a laser beam. The general disadvantage of such erasable structures is a low signal-to-noise ratio because there is no fundamental modification of the structure of the absorbent layer material.